Electrode for electrolysis and electrolysis unit

ABSTRACT

There are disclosed an electrode for electrolysis capable of efficiently forming ozone by electrolysis of an electrolytic solution (e.g., water) at ordinary temperature with a low current density, and an electrolysis unit using the electrode. The electrode for electrolysis includes a substrate and a surface layer formed on the surface of the substrate, and the surface layer is made of an amorphous insulator, for example, a thin film of amorphous tantalum oxide, amorphous tungsten oxide or amorphous aluminum oxide.

BACKGROUND OF THE INVENTION

The present invention relates to an electrode for electrolysis for usein an industrial or household electrolysis process.

In general, ozone is a substance having a very strong oxidizing power,and it is expected that water in which ozone is dissolved, so-calledozone water is applied to a broad range of cleaning sterilizationtreatment of water and sewage, food and the like, and a cleaningtreatment of a semiconductor device manufacturing process. As methodsfor forming the ozone water, there are known a method for dissolving, inwater, ozone formed by irradiation with an ultraviolet ray or electricdischarge, a method for forming ozone in water by electrolysis of thewater, and the like.

In Japanese Patent Application Laid-Open No. 11-77060 (Patent Document1), an ozone water forming device is disclosed which includes ozoneforming means for forming an ozone gas with an ultraviolet lamp and atank to store water, whereby the formed ozone gas is supplied to thewater in the tank to form the ozone water. Additionally, in JapanesePatent Application Laid-Open No. 11-333475 (Patent Document 2), an ozonewater forming device is disclosed which mixes an ozone gas formed by adischarge type ozone gas forming device with water at a predeterminedratio by a mixing pump, in order to efficiently dissolve the ozone gasin the water.

However, in the above-mentioned ozone water forming method forgenerating the ozone gas by the ultraviolet lamp or the discharge systemdescribed above to dissolve this ozone gas in the water, the ozone gasforming device, an operation for dissolving the ozone gas in the waterand the like are required, so that the device is liable to becomecomplicated. The method is a method for dissolving the formed ozone gasin the water, and hence it has a problem that it is difficult toefficiently form the ozone water having a desired concentration.

In Japanese Patent Application Laid-Open No. 2002-80986 (Patent Document3), as a method for solving the above-mentioned problem, a method forforming ozone in water by the electrolysis of the water is disclosed. Insuch a method, an electrode for forming ozone is used which isconstituted of an electrode substrate material formed of a porous bodyor a mesh-like body, and an electrode catalyst including an oxide of aplatinum group element or the like.

Moreover, in Japanese Patent Application Laid-Open No. 2007-016303(Patent Document 4), it is disclosed that model tap water as anelectrolytic solution is electrolytically treated with an electrode forelectrolysis including a surface layer made of a dielectric materialsuch as tantalum oxide, to form ozone.

However, in the method disclosed in Patent Document 3 described above,diamond is used as an electrode substance, and hence there is a problemthat cost of the device itself soars.

Moreover, in the method for forming the ozone water by the electrolysisof water as disclosed in Patent Document 3, the platinum group elementis a standard anode material, and has a characteristic that the elementis hardly dissolved in an aqueous solution which does not include anyorganic substance. However, the element as the electrode for formingozone has a low ozone forming efficiency, and it is difficult toefficiently form the ozone water by an electrolysis process. In suchozone water formation by the electrolysis process using the conventionalelectrode for forming ozone, the electrolysis for the ozone formationrequires a high current density of 1 A/cm² or more, and an electrolyteneeds to be set to a low temperature. This raises a problem that veryhigh energy is consumed. Furthermore, platinum is expensive. When leaddioxide is used instead of platinum, there is a problem of toxicity.

Furthermore, even when the electrode for electrolysis disclosed inPatent Document 4 described above is used, ozone is formed, but furtherimprovement of an ozone forming current efficiency has been demanded.

SUMMARY OF THE INVENTION

The present invention has been developed in order to solve aconventional technical problem, and an object thereof is to provide anelectrode for electrolysis capable of efficiently forming ozone byelectrolysis of water with a low current density.

An electrode for electrolysis according to the invention of a firstaspect comprises a substrate and a surface layer formed on the surfaceof the substrate, characterized in that the surface layer is anamorphous insulator.

The electrode for electrolysis according to the invention of a secondaspect is characterized in that in the above invention, the insulator isan oxide of a single metal or a composite metal oxide.

The electrode for electrolysis according to the invention of a thirdaspect is characterized in that in the above inventions, the insulatoris tantalum oxide or tungsten oxide.

The electrode for electrolysis according to the invention of a fourthaspect is characterized in that in the inventions of the first andsecond aspects, the insulator is aluminum oxide.

The electrode for electrolysis according to the invention of a fifthaspect is characterized in that in the above inventions, a thickness ofthe surface layer is in a range of 20 nm or more to 2000 nm or less.

The electrode for electrolysis according to the invention of a sixthaspect is characterized in that in the above inventions, the substrateis provided with an intermediate layer positioned on an inner side ofthe surface layer and formed of a metal which is not easily oxidized onthe surface of the substrate.

An electrolysis unit of the invention of a seventh aspect ischaracterized in that an anode having water permeability is constitutedof the electrode for electrolysis according to the above inventions, andthe anode and a cathode having water permeability are arranged on bothsurfaces of a cation exchange film.

According to the invention of the first aspect, in the electrode forelectrolysis including the substrate and the surface layer formed on thesurface of the substrate, the surface layer is the amorphous insulator,so that ozone can efficiently be formed by the electrolysis of anelectrolytic solution with a low current density by use of the electrodeas the anode.

In particular, unlike the conventional technology, the temperature ofthe electrolytic solution does not have to be especially set to a lowtemperature, and the high current density is not required, so that powerconsumption required for the ozone formation can be reduced.

According to the invention of the second aspect, in the above invention,the insulator is the oxide of the single metal or the composite metaloxide. In particular, as in the invention of the third aspect, theinsulator is tantalum oxide or tungsten oxide. In consequence, an emptylevel around a bottom of a conduction band at an energy level higherthan Fermi level as much as about a half of a band gap receiveselectrons from an electrolyte, and owing to the electrons, an oxygenforming reaction is suppressed as compared with a case where the surfacelayer is made of a conductor, a crystallized metal oxide or the like.Instead, an ozone forming reaction is more efficiently caused.

Therefore, the electrons move with a higher energy level, whereby anozone forming efficiency for causing the ozone forming reaction can beraised.

According to the invention of the fourth aspect, in the aboveinventions, the insulator is aluminum oxide, so that the electrode forelectrolysis according to the above inventions can be made of acomparatively inexpensive material, and production cost can be reduced.Moreover, any toxic substance such as lead dioxide is not used, wherebyan environmental load can be reduced.

According to the invention of the fifth aspect, in the above inventions,the thickness of the surface layer is in a range of 20 nm or more to2000 nm or less, so that the surface layer can be made of a thin film,and the electrons can move in the electrode via impurities of thesurface layer or Fowler-Nordheim tunneling. Therefore, owing to anelectrode reaction in the anode, the empty level around the bottom ofthe conduction band at the energy level higher than Fermi level as muchas about the half of the band gap can receive the electrons from theelectrolyte, and the movement of the electrons is caused with the higherenergy level, whereby the electrolysis can be performed with the lowcurrent density, and ozone can efficiently be formed.

According to the invention of the sixth aspect, in the above inventions,the substrate is provided with the intermediate layer positioned on theinner side of the surface layer and formed of the metal which is noteasily oxidized on the surface of the substrate. Therefore, theelectrode reaction can be caused with the high energy level in thesurface of the surface layer. In consequence, ozone can efficiently beformed with a lower current density.

In particularly, according to such inventions, the intermediate layer isformed of the metal which is not easily oxidized on the surface of thesubstrate. Therefore, when the electrolysis is performed with theelectrode, it is possible to avoid a disadvantage that the substratesurface is oxidized and non-conducted. In consequence, durability of theelectrode can be improved. As compared with the whole substrate is madeof the material constituting the intermediate layer, the production costcan be reduced. Even in such a case, ozone can similarly efficiently beformed.

In the electrolysis unit according to the invention of the seventhaspect, the anode having the water permeability is constituted of theelectrode for electrolysis according to the above inventions, and theanode and the cathode having the water permeability are arranged on boththe surfaces of the cation exchange film. Therefore, protons move in thecation exchange film, whereby even when the electrolytic solution ispure water, ozone can efficiently be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of an electrode for electrolysisaccording to the present invention (Examples 1, 3);

FIG. 2 is a flow chart of a manufacturing method of the electrode forelectrolysis according to the present invention (Examples 1, 3);

FIG. 3 shows an X-ray diffraction pattern of the electrode forelectrolysis according to the present invention (Example 1);

FIG. 4 is a schematically explanatory view of an electrolysis deviceaccording to the present invention;

FIG. 5 is a diagram showing an ozone forming current efficiency in acase where the electrode for electrolysis prepared on conditions is used(Example 1);

FIG. 6 is a flow chart of a manufacturing method of an electrode forelectrolysis according to another example (Example 2);

FIG. 7 is a cross sectional view of the electrolysis according to theexample (Example 2);

FIG. 8 is an X-ray diffraction pattern of the electrode for electrolysisaccording to the present invention (Example 2);

FIG. 9 is an X-ray diffraction pattern of the electrode for electrolysisaccording to the present invention (Example 2);

FIG. 10 is a diagram showing an ozone forming current efficiency in acase where the electrode for electrolysis prepared on conditions is used(Example 2);

FIG. 11 is an X-ray diffraction pattern of the electrode forelectrolysis according to the present invention (Example 3);

FIG. 12 is a diagram showing an ozone forming current efficiency in acase where the electrode for electrolysis prepared on conditions is used(Example 3); and

FIG. 13 is a schematic explanatory view of an electrolysis unit to whichthe electrode for electrolysis according to the present invention isapplied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferable embodiment of an electrode for electrolysis according tothe present invention will hereinafter be described with reference tothe drawings. FIG. 1 is a cross sectional view of an electrode 1 forelectrolysis of the present invention. As shown in FIG. 1, the electrode1 for electrolysis is constituted of a substrate 2, a close contactlayer 3 formed on the surface of the substrate 2, an intermediate layer4 formed on the surface of the close contact layer 3, and a surfacelayer 5 formed on the surface of the intermediate layer 4. In theelectrode 1 for electrolysis, the substrate 2 is provided with atitanium plate 6 as an electric conductor, and conduction can berealized between the titanium plate 6 and the intermediate layer 4 via asilver paste 7 as a conductive material. Furthermore, this silver paste7 and the titanium plate 6 are coated with a seal material 8, and thisdoes not contribute to electrolysis. It is to be noted that a way torealize the conduction is not limited to this example.

In the present invention, the substrate 2 is made of a conductivematerial of, for example, platinum (Pt), a valve metal such as titanium(Ti), tantalum (Ta), zirconium (Zr) or niobium (Nb), an alloy of two ormore of these valve metals, silicon (Si) or the like. In particular, Sihaving the surface thereof treated so as to be flat is used in thesubstrate 2 for use in the present embodiment.

The close contact layer 3 is formed on the surface of the substrate 2 soas to improve a close contact property between the substrate 2 and theintermediate layer 4 formed of, for example, platinum on the surface ofthe close contact layer 3, and the close contact layer is made oftitanium oxide, titanium nitride or the like. It is to be noted that inthe present embodiment, titanium oxide is used.

The intermediate layer 4 is made of a metal which is not easilyoxidized, for example, platinum or gold (Au), a conductive metal oxidesuch as iridium oxide, palladium oxide or ruthenium oxide, or an oxidesuperconductor. Alternatively, the intermediate layer is made of a metalwhich is oxidized but has conductivity, for example, ruthenium (Ru),rhodium (Rh), palladium (Pd), iridium (Ir) or silver (Ag) included inplatinum group elements. It is to be noted that the metal oxide is notlimited to the oxide beforehand constituting the intermediate layer 4,and may include a metal oxide obtained by electrolytic oxidization.

However, when the intermediate layer 4 is made of the metal oxide havingthe conductivity, for example, iridium oxide or the like, the conductoris adversely affected by oxygen atoms constituting the metal oxide.Therefore, it is preferable that the intermediate layer 4 is made of themetal which is not easily oxidized. In the present embodiment, theintermediate layer 4 is made of platinum.

It is to be noted that when the substrate 2 is made of platinum,needless to say, the surface of the substrate 2 is also made ofplatinum, so that the intermediate layer 4 does not have to beespecially constituted. However, when the substrate 2 is made ofplatinum in this manner, steep rise of cost is incurred. Therefore, itis industrially preferable that the substrate 2 is made of aninexpensive material, and the intermediate layer 4 made of a noble metalor the like is formed on the surface of the substrate 2. There is notany special restriction on the above constitution, as long as thesubstrate 2 is made of a substance which does not have any conductivity,for example, a glass plate and at least a contact surface between thesubstrate 2 and the surface layer 5 described later is coated with amaterial having the conductivity. This can also suppress steep rise ofcost required for the material for use in constituting the substrate 2.

Moreover, the surface layer 5 is an amorphous (an infinite form,non-crystalline) insulator provided together with the intermediate layer4 so as to coat the intermediate layer 4. In the present embodiment, theinsulator is made of tantalum oxide (TaOx), tungsten oxide (WOx) oraluminum oxide (AlOx) in the form of a layer on the surface of thesubstrate 2. This surface layer 5 is formed into a thin film having apredetermined thickness above 0 to 1 mm or less, preferably 20 nm or2000 nm in the present embodiment.

It is to be noted that in the present embodiment, examples of theinsulator include amorphous tantalum oxide, tungsten oxide and aluminumoxide, but the insulator is not limited to these examples, and anamorphous oxide of a single metal as an insulator may be used. Specificexamples of the oxide include TiOx, NbOx, HfOx, NaOx, MgOx, KOx, CaOx,ScOx, VOx, CrOx, MnOx, FeOx, CoOx, NiOx, CuOx, ZnOx, GaOx, RbOx, SrOx,YOx, ZrOx, MoOx, InOx, SnOx, SbOx, CsOx, BaOx, LaOx, CeOx, PrOx, NdOx,PmOx, SmOx, EuOx, GdOx, TbOx, DyOx, HoOx, ErOx, TmOx, YbOx, LuOx, PbOxand BiOx. Alternatively, an amorphous composite metal oxide as aninsulator, SiOx, GeOx or the like may be used.

EXAMPLE 1

Next, a manufacturing method of an electrode 1 for electrolysisaccording to Example 1 of the present invention will be described withreference to a flow chart of FIG. 2. First, silicon (Si) constituting asubstrate 2 is pretreated in step S1. Here, it is preferable thatphosphorous (P), boron (B) and the like are introduced as impuritiesinto Si to improve the conductivity. Si having a very flat surface isused. It is to be noted that in the present example, Si is used as thesubstrate 2, but a conductive material may be used.

In the pretreatment, the substrate 2 of Si is treated with 5% ofhydrofluoric acid to remove a native oxide film formed on the surface ofthe substrate 2. In consequence, the surface of the substrate 2 isfurther flattened. It is to be noted that the pretreatment does not haveto be performed. Afterward, the surface of the substrate 2 is rinsedwith pure water, and then in step S2, the substrate is introduced into achamber of an existing sputtering system to form a film thereon.

In the step S2, a close contact layer 3 for improving a close contactproperty of an intermediate layer 4 as described above is formed on thesurface of the substrate 2. The close contact layer 3 is formed on thesubstrate 2 by a reactive sputtering process. The close contact layer 3is made of titanium oxide, so that the film is formed at roomtemperature for ten minutes on conditions that Ti is used as a firsttarget, a supply power is 6.17 W/cm², an oxygen partial pressure is 52%(Ar:O₂ 24:26) and a film forming pressure is 0.6 Pa. In consequence, theclose contact layer 23 of titanium oxide having a thickness of about 50nm is formed on the surface of the substrate 2. It is to be noted thatin the present example, as a method for forming a film of the closecontact layer 3, the reactive sputtering process is used, but thepresent invention is not limited to this example. For example, asputtering process, a CVD process, an ion plating process, a platingprocess, or a combination of one of these processes and thermaloxidation may be used.

Subsequently, in step S3, the intermediate layer 4 is formed on thesurface of the substrate 2 provided with the close contact layer 3. Theintermediate layer 4 is formed on the surface of the substrate 2 by asputtering process. In the present example, the intermediate layer 4 ismade of platinum, so that the film is formed at room temperature forabout one minute and eleven seconds on conditions that Pt (80 mmφ) isused as a first target, a supply power is 4.63 W/cm², and an Ar gaspressure is 0.7 Pa. In consequence, the intermediate layer 4 having athickness of about 200 nm is formed on the surface of the substrate 2provided with the close contact layer 3. It is to be noted that in thepresent example, as a method for forming a film of the intermediatelayer 4, the sputtering process is used, but the present invention isnot limited to this example. For example, a CVD process, an evaporationprocess, an ion plating process, a plating process or the like may beused.

Subsequently, a surface layer 5 is formed on the surface of thesubstrate 2 provided with the intermediate layer 4. In the presentexample, the surface layer 5 is formed using a spin coat process, sothat the surface of the substrate 2 provided with the intermediate layer4 is coated with an organic aluminum compound solution as a surfacelayer constituting material. In the present example, the surface layer 5is made of aluminum oxide, so that an organic aluminum compound is usedin which a functional group such as a hydroxyl group, an aldehyde group,an alkyl group, a carboxyl group or an alkoxyl group is coordinated inaluminum having a coordination number of 3. Moreover, it is preferablethat aluminum in this organic aluminum compound solution is in a rangeof about 0.4 wt % to 3 wt %. It is to be noted that in the presentexample, the organic aluminum compound solution is used as the surfacelayer constituting material, but the present invention is not limited tothis example. An aluminum-containing compound from which a substanceother than aluminum can be removed by calcinating, for example, aluminumchloride, aluminum bromide, aluminum iodide or the like may be used.

Then, in step S4, the surface constituting material is dripped on thesurface of the substrate 2 provided with an intermediate layer 4 to forma thin film by a spin coat process. In the present example, conditionsof the spin coat process are set to five seconds at 1000 rpm, 15 secondsat 3000 rpm. Afterward, the surface of the substrate is dried in anenvironment at room temperature and then 200° C. for ten minutes (stepS5). In consequence, a surface layer 5 is formed of the surface layerconstituting material including the aluminum compound on the surface ofthe intermediate layer 4 of the substrate 2.

Afterward, in step S6, the substrate 2 provided with the intermediatelayer 4 and the surface layer 5 is calcinated (annealed) at 400° C. to900° C. in a muffle furnace, at 600° C. in atmospheric air for tenminutes to obtain the electrode 1 for electrolysis. In consequence, thesurface layer constituting material applied to the surface of theintermediate layer 4 is uniformly applied aluminum oxide. In the presentexample, the present film forming operation is performed once, wherebythe calcinated and formed surface layer 5 of aluminum oxide has athickness of about 25 nm. It is to be noted that the film formingoperation may be repeated as much as a plurality of times to set thethickness of the surface layer 5 to about 20 nm to 2000 nm.

The surface layer 5 of the electrode 1 for electrolysis obtained asdescribed above is all aluminum oxide. That is, the surface layerconstituting material includes an aluminum-containing compound, forexample, an organic aluminum compound in which a plurality of functionalgroups are coordinated in addition to aluminum. Alternatively, thematerial includes aluminum chloride, aluminum bromide, aluminum iodideor the like. The material is calcinated, whereby substances other thanaluminum, that is, functional groups of organic substances, chloride,bromine and the like are removed. On the other hand, aluminum reactswith oxygen in the atmosphere to form aluminum oxide.

FIG. 3 shows an X-ray diffraction pattern of the surface layer 5 of theelectrode 1 for electrolysis obtained as described above. It is to benoted that in FIG. 3, the electrode 1 for electrolysis is constituted onconditions that a calcinating temperature in constituting the surfacelayer 5 are 700° C., 750° C., 800° C., 850° C. and 900° C. In general,X-ray diffraction (XRD) is used in analysis of a crystal structure,whereby the crystal structure of aluminum oxide constituting the surfacelayer 5 can be analyzed. In the present example, the structure wasobserved using an X-ray diffraction apparatus (D8 Discover manufacturedby Bruker AXS Co.).

According to the observation, diffraction peaks (2θ) shown in an X-raydiffraction pattern of the surface layer 5 of the electrode 1 forelectrolysis obtained in the present example were about 36.1°, about 38°and about 39.6° regardless of the calcinating temperature at which theelectrode 1 was constituted. In general, as the crystal structure ofaluminum oxide, hexagonal system of α-alumina, β-alumina or the like isknown, but diffraction peaks (2θ) of 35.15°, 57.50° and 43.36° inherentin aluminum oxide (Al₂O₃) were not present in any X-ray diffractionpattern of the surface layer 5 of the electrode 1 for electrolysis.Therefore, it is seen that aluminum oxide forming the surface layer 5 ofthe electrode 1 for electrolysis by the above method does not have anycrystal structure, has an infinite form, and is, so-called amorphous. Itis to be noted that in this case, the diffraction peak around 36.1° is apeak of titanium oxide (101) constituting a close contact layer 3, andthe diffraction peak around 39.6° is a peak of platinum (111)constituting the intermediate layer 4.

It is to be noted that in the present example, the surface layer 5 isformed of amorphous aluminum oxide by coating the surface of thesubstrate (the surface of the intermediate layer 4 in the presentexample) with a surface layer constituting material including analuminum compound by a spin coat process to calcinate the material at apredetermined temperature, but the method constituting the surface layer5 with amorphous aluminum oxide is not limited to this example.

As another method, there is a method for forming the surface layer 5 bya thermal CVD process. In this thermal CVD process, the close contactlayer 3 and the intermediate layer 4 are successively formed on thesurface of the substrate 2 in the same manner as in the above example.Afterward, the organic aluminum compound as the surface layerconstituting material is vaporized, and guided to a reaction tube by useof an appropriate carrier gas to perform a chemical reaction on thesurface of the substrate 2 heated to a high temperature of, for example,500° C. to 900° C., preferably 600° C. to 800° C.

In consequence, with regard to the substances excluding aluminum in theorganic aluminum compound as the surface layer constituting material,for example, an organic substance is removed from the surface of thesubstrate 2 heated to the high temperature, and only aluminum reactswith oxygen in the atmosphere to form aluminum oxide on the surface ofthe substrate 2. Aluminum oxide formed on the surface of the substrate 2(in actual, the surface of the intermediate layer 4) constitutes anamorphous thin film (an aluminum oxide film).

It is to be noted that in addition to this method, examples of themethod for constituting the surface layer 5 of amorphous aluminum oxideinclude a dip process.

It is to be noted that in the present example, the close contact layer 3made of titanium oxide is formed on the surface of the substrate 2 madeof Si. Therefore, platinum constituting the intermediate layer 4 isdirectly diffused in the substrate 2 to form platinum silicide, and itcan be prevented that the substrate surface is oxidized andnon-conducted during electrolysis. The close contact layer 3 of titaniumoxide can improve a close contact property between platinum constitutingthe intermediate layer 4 and the substrate 2. In consequence, durabilityof the electrode 1 can be improved.

(Electrolysis Method by use of Electrode for Electrolysis and Evaluationof Electrode)

Next, formation of ozone by electrolysis using the electrode 1 forelectrolysis manufactured as described above will be described withreference to FIGS. 4 and 5. FIG. 4 is a schematically explanatory viewof an electrolysis device 10 to which the electrode 1 for electrolysisis applied, and FIG. 5 is a diagram showing an ozone forming currentefficiency in a case where the electrode for electrolysis prepared onconditions is used.

The electrolysis device 10 is constituted of a treatment tank 11, theelectrode 1 for electrolysis as an anode, an electrode 12 as a cathode,and a power source 15 which applies a direct current to the electrodes1, 12. Then, a cation exchange film (a diaphragm: Nafion (trade name)manufactured by Dupont) 14 is provided so as to be positioned betweenthese electrodes 1 and 12, and divides the inside of the treatment tank11 into one region where the electrode 1 is present and the other regionwhere the electrode 12 is present. Moreover, a stirring device 16 isprovided in a region in which the electrode 1 for electrolysis as theanode is immersed.

Furthermore, model tap water 13 as an electrolytic solution is receivedin this treatment tank 11. It is to be noted that in an experiment ofthe present example, the model tap water is used as the electrolyticsolution, but the cation exchange film is provided, whereby even in acase where pure water is treated, a substantially similar effect isobtained. It is to be noted that the electrolytic solution for use inthe experiment is an aqueous solution model tap water, and a componentcomposition of this model tap water 13 includes 5.75 ppm of Na⁺, 10.02ppm of Ca²⁺, 6.08 ppm of Mg²⁺, 0.98 ppm of K⁺, 17.75 ppm of Cl⁻, 24.5ppm of SO₄ ²⁻ and 16.5 ppm of CO₃ ²⁻.

The electrode 1 for electrolysis is provided by the above-mentionedmanufacturing method, a thickness of the surface layer 5 of theelectrode 1 for electrolysis is about 25 nm, and a calcinatingtemperature in forming the surface layer 5 is 600° C. For comparison,there are used an electrode for electrolysis (formed of AlOx bysputtering) in which the surface layer 5 is formed of aluminum oxide bya sputtering process instead of the spin coat process, an electrode forelectrolysis (spin-coated with TaOx) in which the surface layer 5 isformed of tantalum oxide (TaOx) by the spin coat process, and anelectrode for electrolysis (spin-coated with TiOx) in which the surfacelayer 5 is formed of titanium oxide (TiOx) by the spin coat process.

In the electrode for electrolysis formed of AlOx by the sputtering, thesurface layer 5 is formed on the surface of the intermediate layer 4formed in the same manner as in the above example, so that a target isthe surface layer constituting material of Al, an rf power is set to 100W, an Ar gas pressure is set to 0.9 Pa, and a distance between thesubstrate 2 and the target is set to 60 mm, to execute film formation atroom temperature. Afterward, the substrate 2 provided with the surfacelayer 5 is obtained by executing thermal oxidation at 600° C. in amuffle furnace in the atmospheric air for 30 minutes.

In the electrode for electrolysis spin-coated with TaOx, the surfacelayer 5 of tantalum oxide is formed on the surface of the intermediatelayer 4 formed by a method similar to the present example, by the spincoat process on similar conditions. Then, the electrode is obtained bycalcinating the surface layer at a temperature of 600° C. in theatmospheric air for ten minutes. It is to be noted that a thickness ofthe surface layer 5 is about 25 nm.

In the electrode for electrolysis spin-coated with TiOx, the surfacelayer 5 of titanium oxide is similarly formed on the surface of theintermediate layer 4 by the spin coat process on the similar conditions.Then, the electrode is obtained by calcinating the surface layer at atemperature of 600° C. in the atmospheric air for ten minutes. It is tobe noted that a thickness of the surface layer 5 is about 50 nm. Thesurface layer 5 formed on the conditions is made of titanium oxidehaving an anatase type crystal structure.

It is to be noted that the film thicknesses of the surface layers of theabove electrodes for electrolysis are obtained by conversion substratedon carried amounts of Al, Ta and Ti acquired by evaluation with a X-rayfluorescence analysis device (JSX-3220ZS Element Analyzer manufacturedby JEOL Ltd.).

On the other hand, platinum is used in the electrode 12 as the cathode.Alternatively, the electrode may be constituted of an insolubleelectrode in which platinum is calcinated on the surface of a titaniumsubstrate, a platinum-iridium-substrated electrode for electrolysis, acarbon electrode or the like.

According to the above constitution, 150 ml of model tap water 13 isreceived in each region of the treatment tank 11, and the electrode 1for electrolysis and the electrode 12 are immersed in the model tapwater, respectively. It is to be noted that a distance between theelectrodes is 10 mm. Then, the power source 15 applies a constantcurrent with a current density of about 25 mA/cm² to the electrode 1 forelectrolysis and the electrode 12. Moreover, a temperature of the modeltap water 13 is +15° C.

In the present example, to evaluate an amount of ozone to be formed byeach electrode for electrolysis, an amount of ozone formed in the modeltap water 13 after the electrolysis for five minutes on the aboveconditions is measured by an indigo process (DR4000 manufactured by HACHCo.), and a ratio of a charge which has contributed to the ozoneformation with respect to the total amount of the supplied charge, thatis, an ozone forming current efficiency is calculated.

As shown in FIG. 5, in the experiment, in a case where the electrode 1for electrolysis prepared in the present example (the surface layer 5was made of AlOx by the spin coat process) was used, the ozone formingcurrent efficiency was about 5.64%. On the other hand, when the surfacelayer 5 of AlOx was constituted by the sputtering process, the ozoneforming current efficiency was about 4.0%. In consequence, it has beenseen that the ozone forming current efficiency is high in a case wherethe surface layer 5 is constituted by the spin coat process as comparedwith a case where the surface layer 5 is constituted by the sputteringprocess.

Moreover, when the surface layer 5 was made of another material such asTaOx by the spin coat process (in the experiment, the surface layer ofthe electrode for electrolysis was made of crystallized tantalum oxide),the ozone forming current efficiency was about 1.5%. When the layer wasmade of TiOx (in the experiment, the surface layer of the electrode forelectrolysis was made of titanium oxide having the anatase type crystalstructure), the ozone forming current efficiency was about 0.3%. It hasbeen seen that even in a case where the surface layer 5 is formed into asubstantially equal film thickness by a similar method, when the surfacelayer 5 is made of AlOx, the ozone forming current efficiency isremarkably high as compared with a case where the surface layer is madeof TaOx (crystallized tantalum oxide in the experiment) or TiOx(crystallized titanium oxide in the experiment).

It is seen from the above experiment result that ozone can be formed inthe electrolytic solution even by the electrolysis of the electrolyticsolution by use of each electrode for electrolysis as the anode.However, in a case where the electrode 1 for electrolysis having thesurface layer 5 of AlOx formed by the spin coat process of the presentexample is used, the ozone forming current efficiency is remarkably highas compared with a case where the surface layer 5 is formed of anothermaterial by another process. This is supposedly because the thin-filmsurface layer 5 of amorphous aluminum oxide is formed on the surface ofthe substrate 2 (actually the intermediate layer 4) by the spin coatprocess on the conditions.

In particular, a thin film of amorphous aluminum oxide is formed into athickness of 20 nm to 2000 um, so that electrons move to theintermediate layer 4 made of a conductive material via an impurity levelin the surface layer 5 or Fowler-Nordheim tunneling.

Usually, when a metal electrode is used as the electrode forelectrolysis, an empty level right above Fermi level receives theelectrons from an electrolyte, whereby an electrode reaction in theanode preferentially causes an oxygen forming reaction. When the surfacelayer 5 is made of the crystallized metal oxide, a metal segregates in agrain boundary between crystals, and a current flows. Even in this case,the empty level right above the Fermi level receives the electrons fromthe electrolyte, whereby the oxygen forming reaction is preferentiallycaused by the electrode reaction in the anode.

On the other hand, in a case where the electrode 1 for electrolysisprovided with the surface layer 5 is used as in the example, the surfacelayer 5 is made of amorphous aluminum oxide, so that an empty levelaround a bottom of a conduction band having an energy level higher asmuch as an about half of a band gap than the Fermi level receives theelectrons from the electrolyte. Owing to the electrons, the oxygenforming reaction is suppressed unlike the above case, and instead anozone forming reaction is more efficiently caused.

Therefore, in a case where the electrode 1 for electrolysis according tothe present invention is used, it is supposed that the electrons move ata higher energy level to cause the ozone forming reaction, and an ozoneforming efficiency rises as compared with a case where the electrode forelectrolysis of platinum or the like, or the electrode for electrolysisprovided with the surface layer of crystallized tantalum oxide ortitanium oxide is used.

In consequence, a current having a predetermined low current density of0.1 mA/cm² to 2000 mA/cm², preferably 1 mA/cm² to 1000 mA/cm² is appliedto the electrode 1 for electrolysis, whereby ozone can efficiently beformed. Even when the temperature of the electrolytic solution is notespecially set to a low temperature and is set to ordinary temperatureof +15° C. as in the present example, ozone can efficiently be formed.Therefore, power consumption required for the ozone formation can bereduced.

Moreover, the surface layer 5 of the electrode 1 capable of realizingthe efficient ozone formation can be formed by the spin coat process asdescribed above, so that productivity can be improved as compared with acase where the layer is formed by a conventional sputtering process.Moreover, the electrode for electrolysis can be manufactured with lowmanufacturing cost, and an inexpensive equipment can be realized. Thesurface layer 5 is formed by the thermal CVD process as described above,whereby satisfactory stability and high production efficiency can berealized. Furthermore, any toxic substance such as lead dioxide is notused, whereby an environmental load can be reduced.

EXAMPLE 2

Next, a manufacturing method of an electrode 21 for electrolysisaccording to Example 2 of the present invention will be described withreference to a flow chart of FIG. 6. It is to be noted that FIG. 7 is aschematic constitution diagram of the electrode 21 for electrolysisobtained by the example. First, in step S11, Si constituting a substrate22 is pretreated in the same manner as in the above example. A materialof the substrate 22 is similar to that of the above example, so thatdescription thereof is omitted. Subsequently, in step S12, the substrateis introduced into a chamber of an existing sputtering device to form afilm.

In the step S12, a close contact layer 23 for improving a close contactproperty of an intermediate layer 24 is formed on the surface of thesubstrate 22 as described above. The close contact layer 23 is formed onthe substrate 22 by a reactive sputtering process in the same manner asin the above example. The close contact layer 23 is made of titaniumoxide, so that the film is formed at room temperature for ten minutes onconditions that Ti is used as a first target, a supply power is 6.17W/cm², an oxygen partial pressure is 52% (Ar:O₂ 24:26) and a filmforming pressure is 0.6 Pa. In consequence, the close contact layer 23made of titanium oxide having a thickness of about 50 nm is formed onthe surface of the substrate 22.

Subsequently, in step S13, the intermediate layer 24 is formed on thesurface of the substrate 22 provided with the close contact layer 23 inthe same manner as in the above example. The intermediate layer 24 isformed on the substrate 22 by a sputtering process. In the presentexample, the intermediate layer 24 is made of platinum, so that the filmis formed at room temperature for about one minute and eleven seconds onconditions that Pt (80 mmφ) is used as a first target, a supply power is4.63 W/cm², and an Ar gas pressure is 0.7 Pa. In consequence, theintermediate layer 24 having a thickness of about 200 nm is formed onthe surface of the substrate 22 provided with the close contact layer23.

Subsequently, a surface layer 25 is formed on the surface of thesubstrate 22 provided with the intermediate layer 24. In the presentexample, the surface layer 25 is formed by a sputtering process. In acase where the surface layer is made of tantalum oxide, the film isformed at room temperature for five to 180 minutes on conditions thatthe target is changed to Ta as a surface layer constituting material, anrf power is 100 W, an Ar gas pressure is 0.9 Pa and a distance betweenthe substrate 22 and the target is 60 mm (step S14). In consequence, thesurface layer 25 having a thickness of about 7 nm to 1000 nm is formedon the surface of the intermediate layer 24 of the substrate 22. It isto be noted that the film thicknesses of the intermediate layer 24 andthe surface layer 25 are obtained by conversion substrated on carriedamounts of Pt and Ta acquired by evaluation with a X-ray fluorescence.

Afterward, in step S15, the substrate 22 provided with the surface layer25 is thermally oxidized at temperatures of 300° C., 400° C., 500° C.and 600° C. in a muffle furnace in the atmospheric air for 30 minutes,to obtain the electrode 21 for electrolysis. In consequence, a tantalummetal constituting the surface layer 25 formed on the surface of theintermediate layer 24 is uniformly oxidized. It is to be noted that thetantalum metal is thermally oxidized to constitute tantalum oxide, sothat a thickness of the surface layer 25 is about 14 nm to 2000 nm.

It is to be noted that here, Ta is an example of the materialconstituting the surface layer 25. However, this material may be changedto W, whereby a tungsten metal constituting the surface layer 25 isthermally oxidized to constitute tungsten oxide.

FIG. 8 shows an X-ray diffraction pattern of the electrode 21 forelectrolysis (the surface layer 25 is made of tantalum oxide) obtainedas described above, and FIG. 9 shows an X-ray diffraction pattern of theelectrode 21 for electrolysis (the surface layer 25 is made of tungstenoxide) obtained as described above. X-ray diffraction is used in thesame manner as in the above example, whereby a crystal structure oftantalum oxide (tungsten oxide) constituting the surface layer 25 can beanalyzed. Even in such an example, the structure was observed using anX-ray diffraction apparatus (D8 Discover manufactured by Bruker AXSCo.).

FIG. 8 shows the X-ray diffraction patterns of the electrode 21 oxidizedat 600° C., 500° C., 400° C. and 300° C. in order from the upside. It isto be noted that for comparison, an X-ray diffraction pattern of anelectrode (having the surface only of Pt) which is not provided with thesurface layer 25 is shown in the bottom. In consequence, in theelectrode 21 oxidized at a temperature of 600° C., a diffraction peak (apeak shown by a solid circle in FIG. 8) inherent in tantalum oxide(Ta₂O₅) and a diffraction peak (a peak shown by * in FIG. 8) inherent inplatinum constituting the intermediate layer 24 are recognized.Therefore, it is seen that the surface layer 25 of crystalline tantalumoxide (Ta₂O₅) is formed on the conditions.

On the other hand, in the electrode 21 oxidized at a temperature of 400°C., a diffraction peak (a peak shown by a open circle in FIG. 8)inherent in tantalum oxide (TaO) and a diffraction peak inherent inplatinum are recognized. Therefore, it is seen that the surface layer 25of crystalline tantalum oxide (TaO) is formed on the conditions.

Moreover, in the electrode 21 oxidized at a temperature of 300° C., adiffraction peak (a peak shown by a black triangle in FIG. 8) inherentin tantalum (Ta) and a diffraction peak inherent in platinum arerecognized. Therefore, it is seen that a part of the surface layer 25remains as tantalum on the conditions.

On the other hand, in the electrode 21 oxidized at a temperature of 500°C., any diffraction peak inherent in tantalum oxide or tantalumdescribed above is not recognized, and the diffraction peak inherent inplatinum and a halo indicating an amorphous state (a non-crystallinestate) are recognized. Therefore, it is seen that the surface layer 25of amorphous tantalum oxide is formed on the conditions. It is to benoted that even in comparison with the X-ray diffraction pattern of theplatinum electrode shown for comparison, it is easily seen that theamorphous state is present in the electrode on the conditions.

FIG. 9 shows the X-ray diffraction patterns of the electrode 21 oxidizedat 600° C., 500° C., 400° C. and 300° C. in order from the upside. It isto be noted that for comparison, an X-ray diffraction pattern of anelectrode (having the surface only of Pt) which is not provided with thesurface layer 25 is shown in the bottom in the same manner as describedabove. According to the patterns, in the electrode 21 oxidized at atemperature of 600° C., 500° C. or 400° C., a diffraction peak (a peakshown by a open circle in FIG. 9) inherent in tungsten oxide (WO₃) and adiffraction peak (a peak shown by * in FIG. 9) inherent in platinumconstituting the intermediate layer 24 are recognized. Therefore, it isseen that the surface layer 25 of crystalline tungsten oxide (WO₃) isformed on the conditions.

On the other hand, in the electrode 21 oxidized at a temperature of 300°C., the above-mentioned diffraction peak inherent in tungsten oxide(WO₃) is not recognized, and the diffraction peak inherent in platinumonly is recognized. Therefore, it is seen that the surface layer 25 ofamorphous tungsten oxide is formed on the conditions.

(Electrolysis Method by use of Electrode for Electrolysis and Evaluationof Electrode)

Next, formation of ozone by electrolysis using the electrode 21 forelectrolysis manufactured as described above will be described withreference to FIG. 10. FIG. 10 is a diagram showing an ozone formingcurrent efficiency in a case where the electrode for electrolysisprepared on the conditions is used. In the drawing, a solid circle showsan ozone forming current efficiency in a case where the surface layer 25is made of tantalum oxide, and a open circle shows an ozone formingcurrent efficiency in a case where the surface layer 25 is made oftungsten oxide. It is to be noted that experiment results are obtainedusing an electrolysis device 10 of the above example, and a constitutionof the device and experiment conditions are similar to those describedabove, so that description thereof is omitted.

According to this experiment, in a case where the surface layer 25 oftantalum oxide was constituted, when the oxidizing temperature was 300°C., the ozone forming current efficiency was about 3.6%. The ozoneforming current efficiencies were about 6.6% at an oxidizing temperatureof 400° C., about 7.2% at an oxidizing temperature of 500° C., and about2.4% at an oxidizing temperature of 600° C. Here, at the oxidizingtemperature of 300° C., 400° C. or 600° C., the surface layer has acrystal structure of tantalum oxide or tantalum. On the other hand, atthe oxidizing temperature of 500° C., amorphous tantalum oxide whichdoes not have any crystal structure is formed as the surface layer 25.

According to such a result, it is seen that in a case where the surfacelayer 25 of tantalum oxide is formed and the surface layer of amorphoustantalum oxide which does not have any crystal structure is formed, theozone forming current efficiency is highest.

Moreover, in a case where the surface layer 25 of tungsten oxide wasconstituted, when the oxidizing temperature was 300° C., the ozoneforming current efficiency was about 6.1%. The ozone forming currentefficiencies were about 2.4% at an oxidizing temperature of 400° C.,about 3.6% at an oxidizing temperature of 500° C., and about 4.2% at anoxidizing temperature of 600° C. Here, at the oxidizing temperature of400° C., 500° C. or 600° C., the surface layer has a crystal structureof tungsten oxide. On the other hand, at the oxidizing temperature of300° C., amorphous tungsten oxide which does not have any crystalstructure is formed as the surface layer 25.

According to such a result, it is seen that in a case where the surfacelayer 25 of tungsten oxide is formed and the surface layer of amorphoustungsten oxide which does not have any crystal structure is formed, theozone forming current efficiency is highest.

EXAMPLE 3

Next, an electrode for electrolysis according to Example 3 of thepresent invention will be described. It is to be noted that amanufacturing method of an electrode 31 for electrolysis obtainedaccording to such an example is similar to that shown in the flow chartof FIG. 2 in Example 1, and a schematic constitution diagram issubstantially similar to FIG. 1, so that detailed description of themanufacturing method is omitted.

That is, in the electrode for electrolysis according to the example, aclose contact layer 3 of titanium oxide is formed on the surface of Siconstituting a substrate by a sputtering process as described above, andan intermediate layer 4 of platinum is formed on the surface of theclose contact layer 3 by the sputtering process.

Subsequently, a surface layer 5 is formed on the surface of a substrate2 provided with the intermediate layer 4. In such an example, thesurface layer 5 is formed by a spin coat process, so that the surface ofthe substrate 2 provided with the intermediate layer 4 is coated with anorganic tantalum compound solution as a surface layer constitutingmaterial. In the present embodiment, the surface layer 5 of tantalumoxide is formed using a Ta(OEt)₅ solution in the present example. It isto be noted that in the present example, ethyl acetate is used as asolvent of the Ta(OEt)₅ solution. It is to be noted that in the presentexample, the Ta(OEt)₅ solution is used as the surface layer constitutingmaterial, but the present invention is not limited to this example.There is not any special restriction on the material, as long as thematerial is a tantalum-containing compound which can be calcinated toremove a substance other than tantalum therefrom, thereby forming a filmof tantalum oxide. In the present example, ethyl acetate is used as thesolvent, but the present invention is not limited to this example, andanother solvent such as an alcohol-substrated solvent may be used.

Then, the surface layer constituting material is dripped on the surfaceof the substrate 2 provided with the intermediate layer 4 to form a thinfilm by the spin coat process. Conditions in the spin coat processaccording to such an example are five seconds with 1000 rpm and 15seconds at 3000 rpm in the same manner as in Example 1. Afterward, thefilm is dried in an environment at room temperature for ten minutes andthen at 200° C. for ten minutes.

Afterward, the substrate 2 provided with the intermediate layer 4 andthe surface layer 5 is calcinated (annealed) at 400° C. to 700° C. in amuffle furnace in the atmospheric air for ten minutes, to obtain theelectrode for electrolysis. In consequence, the surface of theintermediate layer 4 is uniformly coated with tantalum oxide as thesurface layer constituting material.

The surface layer 5 of the electrode 1 for electrolysis obtained asdescribed above is all tantalum oxide. That is, the surface layerconstituting material is a tantalum-containing compound which iscalcinated as described above to remove therefrom substances other thantantalum, that is, functional groups of organic substances and the like.On the other hand, tantalum reacts with oxygen in the atmosphere toconstitute tantalum oxide.

FIG. 11 shows an X-ray diffraction pattern of the electrode 1 forelectrolysis (the surface layer 5 is made of tantalum oxide) obtained asdescribed above. X-ray diffraction is used in the same manner as in theabove examples, whereby a crystal structure of tantalum oxideconstituting the surface layer 5 can be analyzed. Even in such anexample, the structure was observed using an X-ray diffraction apparatus(D8 Discover manufactured by Bruker AXS Co.).

FIG. 11 shows the X-ray diffraction patterns of the electrode 1calcinated at 700° C., 600° C., 500° C. and 400° C. in order from theupside. According to the patterns, in the electrode 1 calcinated at atemperature of 700° C. or 600° C., a diffraction peak (a peak shown by asolid circle in FIG. 11) inherent in tantalum oxide (Ta₂O₅) isrecognized. Therefore, it is seen that the surface layer 5 ofcrystalline tantalum oxide (Ta₂O₅) is formed on the conditions.

On the other hand, in the electrode 1 calcinated at a temperature of500° C. or 400° C., a diffraction peak inherent in tantalum oxide(Ta₂O₅) described above is not recognized, and a halo indicating anamorphous state (a noncrystalline state) is recognized. Therefore, it isseen that the surface layer 5 of amorphous tantalum oxide is formed onthe conditions.

(Electrolysis Method by use of Electrode for Electrolysis and Evaluationof Electrode)

Next, formation of ozone by electrolysis using the electrode 1 forelectrolysis manufactured as described above will be described withreference to FIG. 12. FIG. 12 is a diagram showing an ozone formingcurrent efficiency in a case where the electrode for electrolysisprepared on the conditions is used. It is to be noted that experimentresults are obtained using an electrolysis device 10 of the aboveexample, and a constitution of the device and experiment conditions aresimilar to those described above, so that description thereof isomitted.

According to this experiment, when the calcinating temperature was 400°C., the ozone forming current efficiency was about 7.0%. The ozoneforming current efficiencies were about 12.0% at a calcinatingtemperature of 500° C., about 6.1% at a calcinating temperature of 600°C., and about 4.6% at a calcinating temperature of 700° C. Here, at thecalcinating temperature of 600° C. or 700° C., the surface layer has acrystal structure of tantalum oxide. On the other hand, at thecalcinating temperature of 500° C. or 400° C., amorphous tantalum oxidewhich does not have any crystal structure is formed as the surface layer5.

According to such a result, it is seen that in a case where the surfacelayer of tantalum oxide is formed and the surface layer of amorphoustantalum oxide which does not have any crystal structure is formed, theozone forming current efficiency is high as compared with a case wherethe surface layer 5 of tantalum oxide having a crystal structure isformed.

It is seen from the experiment results of Examples 2 and 3 that anelectrolytic solution may be electrolyzed using either electrode forelectrolysis as an anode to form ozone in the electrolytic solution.However, in a case where the surface layer 5 (25) of amorphous tantalumoxide or amorphous tungsten oxide is formed, an ozone forming efficiencyis high as compared with a case where the surface layer of crystallinetantalum oxide or tungsten oxide is formed.

This is supposedly because a thin film of amorphous tantalum oxide ortungsten oxide is formed, so that electrons move to an intermediatelayer made of a conductive material via impurities in the surface layeror Fowler-Nordheim tunneling.

Moreover, usually, when a metal electrode is used as the electrode forelectrolysis, an empty level right above Fermi level receives theelectrons from an electrolyte, whereby an electrode reaction in theanode preferentially causes an oxygen forming reaction. When the surfacelayer is made of the crystallized metal oxide, a metal segregates in agrain boundary between crystals, and a current flows. Even in this case,the empty level right above the Fermi level receives the electrons fromthe electrolyte, whereby the oxygen forming reaction is preferentiallycaused by the electrode reaction in the anode.

On the other hand, in a case where the electrode for electrolysisprovided with the surface layer as in the above examples is used, thesurface layer is made of an amorphous metal oxide such as amorphoustantalum oxide or tungsten oxide, so that an empty level around a bottomof a conduction band having an energy level higher as much as an abouthalf of a band gap than the Fermi level receives the electrons from theelectrolyte. Owing to the electrons, the oxygen forming reaction issuppressed unlike the above case, and instead an ozone forming reactionis more efficiently caused.

Therefore, in a case where the electrode for electrolysis according tothe above examples is used as the anode, it is supposed that theelectrons move at a higher energy level to cause the ozone formingreaction, and an ozone forming efficiency rises as compared with a casewhere the electrode for electrolysis of platinum or the like, or theelectrode for electrolysis provided with the surface layer ofcrystallized tantalum oxide (the crystallized metal oxide) is used.

In consequence, a current having a predetermined low current density of0.1 mA/cm² to 2000 mA/cm², preferably 1 mA/cm² to 1000 mA/cm² is appliedto the electrode 1 for electrolysis, whereby ozone can efficiently beformed. Even when the temperature of the electrolytic solution is notespecially set to a low temperature and is set to ordinary temperatureof +15° C. as in the present example, ozone can efficiently be formed.Therefore, power consumption required for the ozone formation can bereduced.

Moreover, the surface layer 5 of the electrode 1 capable of realizingthe efficient ozone formation can be formed by not only the sputteringprocess but also the spin coat process as described above, so thatproductivity can be improved. Moreover, the electrode for electrolysiscan be manufactured with low manufacturing cost, and an inexpensiveequipment can be realized.

Furthermore, as in the above examples, the substrate 2 of Si is providedwith the intermediate layer 4 including at least a metal which is noteasily oxidized, a metal oxide having conductivity or a metal havingconductivity even when oxidized, and the surface layer 5 is furtherformed on the surface of the intermediate layer 4 as described above, sothat the electrons can effectively move in the surface layer 5.Therefore, the electrode reaction can be caused with a high energy levelin the surface of the surface layer 5, and ozone can efficiently beformed with a lower current density.

It is to be noted that in a case where the substrate 2 is made of amaterial similar to that of the intermediate layer 4, that is, amaterial including at least a metal which is not easily oxidized, ametal oxide having conductivity or a metal having conductivity even whenoxidized, it is possible to constitute an electrode capable of similarlyefficiently forming ozone without being especially provided with theintermediate layer 4. However, the substrate 2 is coated with theintermediate layer 4 made of the above material as in the presentinvention, whereby it is possible to realize with low production costthe electrode 1 capable of similarly efficiently forming ozone.

Moreover, the electrode for electrolysis according to the examples ofthe present invention is not limited to the electrode shown in theelectrolysis device 10, and may be used as, for example, an anode for anelectrolysis unit 26 shown in FIG. 13.

That is, the electrolysis unit 26 shown in FIG. 13 is constituted of theelectrode 1 or 21 for electrolysis constituting the anode according tothe above examples, an electrode 28 constituting the cathode, and acation exchange film 29.

The electrode 1 (or 21 as the anode) and the electrode 28 (the cathode)are provided with a plurality of water permeable holes 27A and 28A forsecuring water permeability, respectively. Then, the electrodes 1 and 28are arranged on both surfaces of the cation exchange film (Nafion (tradename) manufactured by Dupont Co. was used in the present example) 29, toconstitute the electrolysis unit 26,

According to such a constitution, the electrolysis unit 26 is immersedin a treatment tank in which an electrolytic solution is received, and aconstant current with a predetermined current density is applied betweenboth the electrodes 1, 28. In consequence, an appropriate zero gap ismaintained between the electrode 1 and the cation exchange film 29 andelectrode 28, and protons move in the cation exchange film 29, wherebyozone can efficiently be formed even when the electrolytic solution ispure water. The water permeable holes 27A and 28A allow a formed gas toflow therethrough, whereby stable ozone formation can be realized.

1. An electrode for electrolysis comprising a substrate and a surfacelayer formed on the surface of the substrate, wherein the surface layeris an amorphous insulator.
 2. The electrode for electrolysis accordingto claim 1, wherein the insulator is an oxide of a single metal or acomposite metal oxide.
 3. The electrode for electrolysis according toclaim 1 or 2, wherein the insulator is tantalum oxide or tungsten oxide.4. The electrode for electrolysis according to claim 1 or 2, wherein theinsulator is aluminum oxide.
 5. The electrode for electrolysis accordingto claim 1, 2, 3 or 4, wherein a thickness of the surface layer is in arange of 20 nm or more to 2000 nm or less.
 6. The electrode forelectrolysis according to claim 1, 2, 3, 4 or 5, wherein the substrateis provided with an intermediate layer positioned on an inner side ofthe surface layer and made of a metal which is not easily oxidized onthe surface of the substrate.
 7. An electrolysis unit in which an anodehaving water permeability is constituted of the electrode forelectrolysis according to claim 1, 2, 3, 4, 5 or 6 and in which theanode and a cathode having water permeability are arranged on bothsurfaces of a cation exchange film.